Compound (V) is an endothelin receptor antagonist and useful for treating various circulatory system diseases such as hypertension, ischemic disorders, cerebral circular disorders, renal disorders, circular insufficiency of various organs, asthma, stroke, cerebral infarction, cerebral edema and the like (Patent Literature 1, Patent Literature 2 etc.). A process for preparing oleanolic acid derivatives, which are intermediates of Compound (V), such as myricerone etc., is disclosed in Patent Literature 3. Additionally, a process for preparing Compound (V) using an oleanolic acid is disclosed in Non-Patent Literature 1 and Non-Patent Literature 2 etc. However, processes described in these literatures need an isolation process of intermediates, different reagents or solvents in each reaction step, environmental harmful reagents or the like and are not necessarily sufficient for industrial manufacturing processes.
A method for reduction of a nitro group of hydroxy-2-nitrobenzaldehyde to an amino group by catalytic reduction is described in Patent Literature 4, but in this method, a reduction process is conducted after an aldehyde group is protected as acetal.    Patent Literature 1 WO92/12991    Patent Literature 2 JP 7-53484 A    Patent Literature 3 JP 7-316188 A    Patent Literature 4 JP 7-1011956 A    Non-Patent Literature 1 Organic Process Research & Development, 1999, vol. 3, p.347–351    Non-Patent Literature 2 Journal of Organic Chemistry, 1997, vol.62, p.960–966